After upgrading Nuxt.js from v2 to v3, we noticed something strange: the number of indexed pages in Google Search Console suddenly dropped by more than half. Everything looked normal—our sitemap and robots.txt were fine. But Googlebot couldn’t fully load the pages, so they were mistakenly treated as “soft 404s”—pages that exist, but Google sees as missing. These issues were hard to detect and even harder to solve. It took us months of testing and investigation. In this article, we share the cause of the soft 404 problem we faced, and how we eventually fixed it.